Multivalent acids have various interesting properties, including their ability to form ionic and/or covalent crosslinks as well as their ability to undergo progressive deprotonation with an increase in pH.
As a specific example, phytic acid, also known as myo-inositol hexakis(di-hydrogen phosphate), inositol hexaphosphoric acid and 1,2,3,4,5,6-cyclohexanehexolphosphoric acid, is a well-known naturally occurring acid with six phosphate functional groups attached to each carbon of a cyclohexane ring, i.e.,
where
Phytic acid has twelve dissociable protons, six of which are reported to be strongly acidic with an approximate pKa value of 1.5, the following three of which are reported to be weakly acidic with pKa values between 5.7 and 7.6, and the final three of which are reported to be very weakly acidic with pKa values greater than 10. See L. Yang et al. Electrochemistry Communications 9 (2007) 1057-1061 and the references cited therein.
Furthermore, certain multivalent acids, including phytic acid, have been shown to have therapeutic capabilities. For example, A. M. Shamsuddin et al., Life Sciences, 61(4), 1997, 343-354 present a review regarding the anticancer effects of phytic acid. See also M. Verghese et al., LWT 39 (2006) 1093-1098. One explanation posited for the anticancer effects of phytic acid is its antioxidant properties. Muraoka et al., Life Sciences 74 (2004) 1691-1700.